Handheld devices such as cell telephones and personal digital assistants (PDAs) are limited by the relatively small size of the display screen. The handheld device is generally small and compact. Correspondingly, the size of the display screen is also small. Space is only available on the screen to display abbreviated or simplistic content. For example, a cellular telephone that receives an e-mail is only capable of displaying a few words. It would be impossible to display an entire Web page on these handheld devices. On the other hand, it is inconvenient to carry around and operate a laptop computer for the benefit of its larger display. Most handheld devices are capable of supplying data to display more information if a larger display were available. As a result, recently a number of solutions have been proposed.
U.S. Pat. No. 6,574,488 discloses a terminal that is portable and detachable from a base (such as a cell phone). The terminal has a separate, larger display. Data exchange by radio frequency (RF) is made possible between the base and the terminal, and e-mail or facsimile data that is received by the base through a telephone circuit is stored in the terminal. A user can remove the terminal from the base and carry it to his room, and display stored e-mail messages or facsimile data there. Similarly, U.S. Pat. No. 6,640,113 discloses an integrated system including a radiotelephone and a touch sensitive display that electronically communicates with the radiotelephone, which can be stored within a slot provided in the radiotelephone housing. The display is removable from the slot for use and communicates with the radiotelephone through a cable or a wireless connection. The separate display may be removable from the cell phone, and may communicate via RF means. A similar concept is disclosed in U.S. Pat. No. 6,327,482 where a mobile radio apparatus includes a display and connector on one side. An auxiliary display is removably connected to the side of the apparatus body with the terminal portion mating with the connector portion of the apparatus body. The auxiliary display connected to the apparatus body assists the main display in displaying data at the time of transmission or receipt. When the apparatus is carried by the user, the auxiliary display is dismounted from the apparatus body.
In order to increase the portability for more convenient handheld operation other solutions have been proposed. U.S. Patent Application 2003/016076 discloses a wireless detachable display for a handheld computing device or cell phone. In order to be more mobile, the display system includes a first power source for the processing unit, and a second power source for the visual display. In one embodiment, the processing unit is attached to the user's belt and as such can include a larger battery. This has the advantage of increasing the battery life of the handheld device containing the display. The visual display is physically separable from the processing unit while displaying information according to communications from the processing unit between the visual display transceiver and the processing unit transceiver.
In order to make a larger display less cumbersome to carry around, U.S. Patent Application 2003/0144034 proposes an interactive, collapsible, multi-media display system for use as a hand-held, portable communications device. The housing containing the display is shaped like a large pen. When the display is not being used, the '034 patent application discloses that it can be rolled up inside the pen housing and unrolled for viewing. The device housing can contain a processor, radio transceiver for transmitting and receiving radio signals, along with a collapsible display that is mechanically coupled to the housing and electrically coupled to the processor. The display can have a surface area that is larger than any cross-sectional area of the housing. The processor can be adapted to extract display data from input radio signals, and to provide a representation of the data to the display. The '034 patent application discloses that an organic light emissive device (OLED) is used for this collapsible device.
Various display technologies have been proposed for the large auxiliary display. Since the display is remote from the small handheld device it needs to either supply its own power or receive power from some other unit. All displays require power, some considerably more than others; and the larger the display is the more power it requires. Power can therefore be an overriding issue in the adaptation of a display technology for a remote display device or a portable communications device. Emissive displays such as OLEDs or backlit displays such as backlit LCDs, which have been proposed for use as remote displays, are undesirable in that they consume a lot of power in generating the light. OLEDs are not bistable. They require continuous application of a voltage in emitting light. OLEDs do not reflect light with the liquid crystal of the display. For many handheld applications OLEDs can further be undesirable because they can be hard to see in bright sunlight.
U.S. Pat. No. 6,348,908 discloses a bistable, reflective gyricon technology used in a remote display powered only by ambient energy. Ambient energy is collected by an ambient energy receiver such as a solar panel that converts the ambient energy into electrical power to operate the controller and the display. Ambient energy can be visible light, and can also be non-visible energy such as, for example, the infrared portion of the electromagnetic spectrum. If a solar cell is used, it must be of sufficient size to generate the desired power. There must be sufficient area on the remote device to contain both the solar panel and the separate components of the display which itself can occupy significant area. In order for the gyricon display to offer high resolution required to display text, images and graphics it employs an active matrix backplane, which adds considerable cost to the device.
Another bistable reflective display technology is disclosed in U.S. Pat. Nos. 6,252,564 and 6,118,426. These devices feature an electrophoretic display that is both powered and controlled using radio frequencies. The system includes an antenna, passive charging circuitry, an active control system, a display, and an energy storage unit. There is also a separate transmitter that provides remote power for the display. The system is meant to be used anywhere it is useful to provide intermittent updates of information. Like the gyricon technology, the electrophoretic technology in these patents employs an active matrix for a high resolution display to show detail required in quality text, photos and graphics, which increases the cost of the display.
While these technologies propose using a remote display device as an auxiliary display to a small handheld device, there remains to be a solution wherein the remote display device: can power itself; does not need extra area on the device to contain a solar panel; does not need an extra transmitter to supply power; does not require an active matrix and resulting increased cost and complexity of the device; and/or is flexible so as to be conformable, rugged and, for example, operational despite being rolled or folded up for easy carrying, while having low power requirements.